Transfer assembly for a hydrocarbon product

ABSTRACT

To increase the safety of a transfer assembly for hydrocarbon products, particularly liquefied natural gas from a production site to a transport vessel ( 8 ) (such as a shuttle tanker), the invention proposes to provide the production site with an outrigger structure ( 10 ) with at the distant end thereof a compacted length of a flexible product transfer hose ( 20 ).

The invention relates to a transfer assembly for transferring ahydrocarbon product, particularly a liquefied natural gas from aproduction site to a transporting vessel (such as a shuttle tanker).

The transfer of hydrocarbon products, particularly liquefied natural gasfrom a production site to a vessel, such as a shuttle tanker is anundertaking which entails many risks. Known is a system commonly calledthe “tandem loading”-system, in which the tanker moors as close aspossible, and parallel to the production site after which the transferof the product is undertaken. Not only the shuttle tankers themselves,carrying the product, constitute a serious hazard but it is clear that acollision between a shuttle tanker and a production site during transferside could easily have catastrophic consequences.

The invention aims to provide a transfer assembly of the kind asreferred to herein before, with which it is possible to provide thelargest practical separation between the production site (or aproduction vessel) and a shuttle tanker, which allows the use of thecommon double walled piping between the production site and the shuttlevessel and which minimizes the risk of gas clouds and vapors which mightescape due to failures in the mechanical off-loading components.

By means of these measures a maximum distance between the productionsite and the transporting vessel can be maintained, so that a maximumsafety is ensured. When not in use the flexible hose is stored on thereel on the end of the outrigger structure; when product is to betransferred the transfer vessel approaches the outrigger, accepts (forinstance by means of a messenger line) the hose end and connects it to areceptacle on the stern of the transfer vessel. The transfer vessel canthan, if necessary, increase the distance to the production side,staying connected to it by means of a common hawser.

It is observed that an outrigger structure for supporting a transferhose, and provided at a production site is known in itself fromWO-A-99/35031, FR-A-2660490 and NL-A-7711419. Providing a compactedlength of hose as a reel structure on the stern of a vessel is knownfrom GB-A-2295372. DE 29 16 489 describes a system for preventingpollution of sea water by oil from a damaged tanker in which a length ofthin-walled hose is accommodated on a reel; in case of damage of acompartment wall the contents of this compartment can be transfered by apumping assembly to the lumen of the hose which is unwound from the reeland therafter floated on the surface of the surrounding water to preventpollution thereof.

The compacted length of hose is preferably stored on a reel.

This allows the transfer vessel to “weathervane” over a certain anglewith respect to the production side, the transfer hose staying alignedwith the movable outer end of the transfer arm.

The invention will be elucidated on the hand of the drawing. Hereinshow:

FIG. 1 a side view of the transfer assembly according to the invention;and

FIG. 2 a top view thereof.

FIG. 1 shows schematically a part of a hydrocarbon production site 2, inthis case a production vessel, floating on the surface 4 of a body ofwater 6. The drawing also shows a shuttle tanker 8, floating on thisbody of water.

The transfer assembly according to the invention, provided on theproduction vessel 2 comprises an outrigger structure 10, being, in fact,an outrigger arm consisting of two parts, a first part 12, rigidlyconnected to one end 2 a of the production vessel 2, and a second armpart 14 connected to the part 12 by means of a vertical hinge structure16. The movable arm carries at its outer end a hose reel 18 on which iswound a length of flexible hose 20. This hose can be the conventionaldouble walled piping, allowing the transfer of gaseous products andliquefied natural gas.

To be put into use the shuttle tanker 8 approaches the production vessel2, whereafter a normal mooring hawser 22 is connected between the end 2a of the production vessel 2 and the bow 8 a of the tanker 8. Thereaftera messenger line 24 is connected between the end of the hose 20 and thevessel end 2 a and is then taken in and connected to the connectingpoint26 on the bow 8 a of the tanker 8. Thereafter sufficient length of hose,schematically indicated with 20 a, is paid out and the transfer of thehydrocarbon products from the production site 2 to the tanker 8 iscommenced.

The arrangement works satisfactory without the vertical hinge 16 betweenthe two arm parts 12 and 14, thus with an entirely rigid arm, but thepresence of this hinge 16 has the advantage that the hose part 20 a andthe center line of the tanker 8 will always stay aligned with the centerline of the arm part 14, thus preventing bending moments on the hose 20there where it enters the reel 18. Damping means (not shown) may beprovided between the two arm ends 12 and 14. Preferably the verticalaxis 16 a of this vertical hinge 16 includes a small angle with thevertical, so that the weight on the reel arrangement 18 will stabilizethe arm part 14 along the center line of the arm part 12, and thus alongthe center line of the production vessel.

1. A transfer assembly for transferring a hydrocarbon product from aproduction site to a transporting vessel, the transfer assemblycomprising: an outrigger structure mounted on the production site abovethe water line, and covering between 30% and 60% of a described safetydistance between the production site and the vessel; and a compactedlength of a flexible product transfer hose at a distant end of thetransfer assembly, wherein an input end of the transfer hose is operableto be connected to a product delivery point, and wherein an outlet endof the transfer hose is operable to be connected to an inlet connectionon the transporting vessel wherein the outrigger structure comprises anarm, divided by at least one hinge with a generally vertical pivot axisinto at least two parts, of which at least an outer one is free to moveover a pre-defined angle with respect to the longitudinal axis of thearm structure.
 2. The transfer assembly according to claim 1, whereinthe hinge axis is inclined over a small angle in the direction of thefree end of the arm.
 3. The transfer assembly according to claim 1,wherein the hydrocarbon product is a liquefied natural gas.
 4. Thetransfer assembly according to claim 1, wherein the transporting vesselis a shuttle tanker.
 5. The transfer assembly according to claim 1,wherein the compacted length of hose is stored on a hose reel.
 6. Thetransfer assembly according to claim 5, wherein the outrigger structurecomprises an arm, divided by at least one hinge with generally verticalpivot axis into at least two parts, of which at least an outer one isfree to move over a pre-defined angle with respect to the longitudinalaxis of the arm structure.
 7. The transfer assembly according to claim6, wherein the hinge axis is inclined over a small angle in thedirection of the free end of the arm.